Powered surgical drill having transducer assembly including at least two rotation sensor devices for use in determining bore depth of a drilled hole

ABSTRACT

A surgical drill for drilling a hole in a workpiece includes a housing, a probe moveably mounted to the housing, and a transducer assembly. The transducer assembly includes a gear coupled to the probe and at least two rotational sensor devices coupled to the gear to determine an amount of movement of a probe relative to a housing to determine a bore depth of the hole. The gear has a reference point having an angular path of rotation about a gear axis subdivided into separate first and second arcuate regions. A first sensor device is configured to detect a rotational position of the reference point in the first arcuate region, and a second sensor device is configured to detect a rotational position of the reference point in at least the second arcuate region, with the first sensor device incapable of detecting the reference point in the second arcuate region.

CROSS REFERENCED APPLICATION

This application is the National Stage of International PatentApplication No. PCT/US2019/030180, filed on May 1, 2019, which claimspriority to and all advantages of U.S. Provisional Patent ApplicationNo. 62/665,024, which was filed on May 1, 2018, the disclosures of whichare specifically incorporated by reference.

BACKGROUND OF THE DISCLOSURE

One type of powered surgical tool, or powered surgical system, used inorthopedic surgery is the surgical drill. This type of tool includes ahousing that contains a motor. A coupling assembly, also part of thedrill, releasably holds a drill bit to the motor so that, upon actuationof the motor, the drill bit rotates. As implied by its name, a surgicaldrill drills bores in the workpiece, such as tissue, against which thedrill bit is applied. One type of surgical procedure in which it isnecessary to drill a bore is a trauma procedure to repair a broken bone.In this type of procedure, an elongated rod, sometimes called a nail, isused to hold the fractured sections of the bone together. To hold thenail in place, one or more bores are driven into the bone. These boresare positioned to align with complementary holes formed in the nail. Ascrew is inserted in each aligned bore and nail hole. The screws holdthe nail in the proper position relative to the bone.

In another type of procedure, an implant, or workpiece, known as a plateis secured to the outer surfaces of the fractured sections of a bone tohold the sections together. Screws hold the plate to the separatesections of bone. To fit a screw that holds a plate to bone it isnecessary to first drill a bore to receive the screw.

As part of a procedure used to drill a screw-receiving bore in a bone,it is desirable to know the end-to-end depth of the bore. Thisinformation allows the surgeon to select the size of a screw that isfitted in the bore hole. If the screw is too short, the screw may notsecurely hold the nail into which the screw is inserted in place. If thescrew is too long, the screw can extend an excessive distance out beyondthe bone. If the screw extends an excessive distance beyond the bone,the exposed end of the screw can rub against the surrounding tissue. Ifthis event occurs, the tissue against which the screw rubs can bedamaged.

Accordingly, an integral part of many bone bore-forming procedures isthe measuring of the depth of the bore.

This measurement is often taken with a depth gauge separate from thedrill. This requires the surgeon, after withdrawing the drill bit fromthe bore, to insert the depth gauge into the bore. Then, based ontactile feedback, the surgeon sets the gauge so the distal end of thegauge only extends to the far opening of the bore. Once these processesare complete, the surgeon reads the gauge to determine the depth of thebore. This measurement is disadvantageous because it is both labor andtime intensive, is reliant upon human element to confirm the measureddepth, and may increase the risk of infection and increase the exposureof the patient to anesthesia.

The present disclosure addresses some of these issues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a surgical system comprising a surgicalinstrument and end effector assembly, the end effector assembly shownhaving a drill bit and a tip protector according to one configuration.

FIG. 2 is a partially-exploded perspective view of the surgical systemof FIG. 1 , with the surgical instrument shown having a measurementmodule, a drive assembly, and a release mechanism spaced from ahandpiece body, and with the end effector assembly removed from thesurgical instrument and shown with the tip protector spaced from adistal cutting tip portion of the drill bit.

FIG. 3 is a partially-exploded perspective view of portions of thesurgical instrument of FIGS. 1-2 , shown with the drive assembly and therelease mechanism spaced from a phantom outline of the handpiece body todepict an actuator assembly.

FIG. 4 is a partial isometric sectional view taken along line 4-4 inFIG. 1 .

FIG. 5 is a sectional view taken longitudinally through the surgicalinstrument of FIGS. 1-5 , with the end effector assembly removed fromthe surgical instrument.

FIG. 6 is a partially-exploded perspective view of the measurementmodule of FIGS. 1-5 .

FIGS. 7A-7C is a partially-exploded front perspective view of the gearand the pair of potentiometers of the measurement module, with thepotentiometers rotated at 180 degrees with respect to one another, andillustrating various positionings of the wiper arms correlated to areference point on the gear.

FIG. 8 is a front view of the gear and the pair of potentiometers of themeasurement module, with the potentiometers rotated at 90 degrees withrespect to one another, and illustrating one positioning of the wiperarms correlated to a reference point on the gear.

FIG. 9 is a logic flow diagram describing a method in for determining abore depth in a workpiece formed by a drill bit attached to the surgicaldrill of FIGS. 1-8 .

FIG. 10 is a logic flow diagram for Step 706 of the logic flow diagramof FIG. 9 .

SUMMARY OF THE DISCLOSURE

A surgical drill for actuating a drill bit is provided. The drillincludes a housing, a probe moveably mounted to said housing and adaptedfor placement against a workpiece, and a transducer assembly. Thetransducer assembly includes a gear coupled to the probe and configuredto rotate more than 360 degrees about a gear axis upon the movement ofthe probe relative to the housing. The gear having a reference pointhaving an angular path of rotation about the gear axis being dividedinto a first arcuate region and a second arcuate region. The firstarcuate region being separate from the second arcuate region. Atransducer comprising at least two potentiometers is also included, witheach of the at least two potentiometers coupled to the gear. A first ofthe at least two potentiometers is configured to detect a rotationalposition of the reference point in the first arcuate region and a secondof the at least two potentiometers is configured to detect therotational position of the reference point in at least the secondarcuate region, the first rotational sensor being incapable of detectingthe reference point in the second arcuate region.

A method for determining a bore depth in a workpiece formed by a drillbit attached to a drill is also provided, with the drill including ahousing, a probe coupled to the housing, and a transducer assemblyincluding a gear coupled to the probe and a transducer including atleast two rotational sensor devices coupled to the gear. The methodincludes the steps of determining a first rotational position of thegear, determining a number of full rotations of the gear in a singlerotational direction about a gear axis from the determined firstrotational position, with each of the full rotations corresponding to apredefined amount of movement of the probe relative to the housing. Themethod also includes determining a second rotational position of thegear, the determined second rotational position the same or differentthan the determined first rotational position, and determining an amountof movement of the probe relative to the housing from the determinedfirst and second rotational position and from the determined number offull rotations of the gear.

The surgical drill may include a housing, a coupling assembly disposedwithin the housing adapted to releasably couple the drill bit, a probemoveably mounted to said housing and adapted for placement againsttissue. The drill may also include a transducer assembly including agear coupled to the probe and configured to rotate more than 360 degreesabout a gear axis upon the movement of the probe relative to thehousing, the gear having a reference point having an angular path ofrotation about the gear axis being divided into a first arcuate regionand a second arcuate region, the first arcuate region being separatefrom the second arcuate region. The transducer assembly may also includea transducer comprising at least two rotational sensor devices, each ofthe at least two rotational sensors fixed rotationally relative to thegear, with the first rotational sensor configured to detect a rotationalposition of the reference point in the first arcuate region and a secondrotational sensor configured to detect the rotational position of thereference point in the second arcuate region. The first rotationalsensor being incapable of detecting the reference point in the secondarcuate region, with the at least two rotational sensors adapted forindependently generating a output signal corresponding to the detectedrotational position of the reference point in said respective first andsecond arcuate region. The drill also includes a controller configuredto receive each of the independently generated output signals and, basedon each of the independently generated output signals, determine thedepth of the bore in the tissue formed by the drill bit.

DETAILED DESCRIPTION

With reference to the drawings, where like numerals are used todesignate like structure throughout the several views, a surgicalsystem, or surgical drill, is shown at 60 in FIGS. 1-2 for performing anoperational function that is typically associated with medical and/orsurgical procedures. In the representative configuration illustratedherein, the surgical system 60 is employed to facilitate penetrating aworkpiece, such as tissue or bone of a patient. As used herein, unlessotherwise indicated, the term workpiece is understood to alternativelyrefer to tissue and/or bone. To this end, the illustrated configurationof the surgical system 60 comprises a handheld surgical instrument 62and an end effector assembly, generally indicated at 64. The endeffector assembly 64, in turn, comprises a drill bit 66 and may alsoinclude a tip protector 68. As is best depicted in FIG. 2 , the drillbit 66 extends generally longitudinally along an axis AX between acutting tip portion, generally indicated at 70, and an insertionportion, generally indicated at 72. The cutting tip portion 70 isconfigured to engage the workpiece, and the insertion portion 72 isconfigured to facilitate releasable attachment of the drill bit 66 tothe surgical instrument 62.

In order to help facilitate attachment of the drill bit 66 to thesurgical instrument 62, in some configurations, the tip protector 68 isconfigured to releasably secure to the cutting tip portion 70 of thedrill bit 66 while concealing at least a portion of the cutting tipportion 70 of the drill bit 66, thereby allowing a user (e.g., asurgeon) of the surgical system 60 to handle and position the drill bit66 safely during attachment to the surgical instrument 62. Once the endeffector assembly 64 has been attached to the surgical instrument 62,the tip protector 68 is subsequently removed from the cutting tipportion 70 of the drill bit 66, and the surgical system 60 can then beutilized to penetrate the workpiece.

Referring now to FIGS. 1-6 , in the representative configurationillustrated herein, the surgical instrument 62 is realized as a handhelddrill with a pistol-grip shaped handpiece body 74 which releasablyattaches to a battery 76 (battery attachment not shown in detail).However, it is contemplated that the handpiece body can have anysuitable shape with or without a pistol grip. While the illustratedsurgical instrument 62 employs a battery 76 which is releasablyattachable to the handpiece body 74 to provide power to the surgicalinstrument 62 utilized to rotate the drill bit 66, it will beappreciated that the surgical instrument 62 may be configured in otherways, such as with an internal (e.g., non-removable) battery, or with atethered connection to an external console, power supply, and the like.Other configurations are contemplated.

In the illustrated configuration, the battery 76 or other power sourceprovides power to a controller 78 (depicted schematically in FIG. 5 )which, in turn, is disposed in communication with an input control 80and an actuator assembly 82 (see also FIG. 3 ). The input control 80 andthe actuator assembly 82 are each supported by the handpiece body 74.The controller 78 is generally configured to facilitate operation of theactuator assembly 82 in response to actuation of the input control 80.The input control 80 has a trigger-style configuration in theillustrated configuration, is responsive to actuation by a user (e.g., asurgeon), and communicates with the controller 78, such as viaelectrical signals produced by magnets and Hall effect sensors. Thus,when the surgeon actuates the input control 80 to operate the surgicalinstrument 62, the controller 78 directs power from the battery 76 tothe actuator assembly 82 which, in turn, generates rotational torqueemployed to rotate the drill bit 66, as described in greater detailbelow. The handpiece body 74, the battery 76, the controller 78, and theinput control 80 could each be configured in a number of different waysto facilitate generating rotational torque without departing from thescope of the present disclosure.

As also shown in FIG. 3 , the actuator assembly 82 generally comprisesan electric motor 84 and a gearset 86 which are each supported withinthe handpiece body 74. The motor 84 is configured to selectivelygenerate rotational torque in response to commands, signals, and thelike received from the controller 78. As is best shown in FIG. 5 , themotor 84 comprises a rotor cannula 88 supported for rotation about theaxis AX by a pair of bearings 90. A drive gear 92 arranged adjacent tothe gearset 86 is coupled to and rotates concurrently with the rotorcannula 88, and is employed to transmit rotational torque to the gearset86. To this end, in the illustrated configuration, the gearset 86 isrealized as two-stage compound planetary arrangement and generallycomprises a ring gear housing 94 which, among other things, rotationallysupports an output hub 96 via a bearing 90, as well as one or moreretaining clips 98, washers 100, and/or seals 102. However, otherconfigurations of the gearset 86 are contemplated.

Further details of the gearset 86 are described, for example, in U.S.patent application Ser. No. 15/887,507, filed on Feb. 2, 2018 andentitled “Drill Bit for Handheld Surgical Instrument, the contents ofwhich are herein incorporated by reference in their entirety, anddescribe wherein the rotation of the drive gear 92 via actuation of themotor 84 effects concurrent rotation of the output hub 96, and whereinthe output hub 96 rotates concurrently with the drill bit 66. Theactuator assembly 82 could be configured in other ways without departingfrom the scope of the present disclosure. By way of non-limitingexample, while the illustrated actuator assembly 82 employs a compoundplanetary arrangement to adjust rotational speed and torque between thedrive gear 92 of the motor 84 and the output hub 96, other types ofgearsets 86 could be utilized in some configurations. Moreover, whilethe illustrated actuator assembly 82 employs an electrically-poweredbrushless DC motor to generate rotational torque, other types of primemovers could be utilized. Other configurations are contemplated.

As noted above, rotational torque generated by the motor 84 effectsrotation of the output hub 96 which, in turn, rotates concurrently withthe drill bit 66. To this end, and as is best shown in FIGS. 2-5 , thesurgical instrument 62 further comprises a drive assembly 114 whichgenerally extends through the various cannulated components of theactuator assembly 82 into splined engagement with the output hub 96 ofthe gearset 86. The drive assembly 114 is configured to facilitatereleasable attachment between the drill bit 66 and the surgicalinstrument 62. The drive assembly 114 generally comprises a drivingcannula 116, a driving head 118, and a driving body 120 which extendsbetween, and rotates concurrently with, the driving cannula 116 and thedriving head 118. The drive assembly 114 is supported for rotation aboutthe axis AX within the handpiece body 74 via splined engagement with theoutput hub 96 adjacent the driving cannula 116, and via an arrangementof bearings 90, snap rings 100, and seals 102 adjacent the driving head118 (see FIG. 6 ).

Further details of the drive assembly 114 are also described, forexample, in U.S. patent application Ser. No. 15/887,507, the contents ofwhich are also herein incorporated by reference in their entirety. Inthe illustrated configuration, the driving head 118 of the driveassembly 114 comprises a coupling, generally indicated at 126, which isprovided to facilitate transmitting rotational torque when the surgicalinstrument 62 is utilized in connection with other applications besidesrotating the drill bit 66 of the present disclosure. More specifically,the illustrated drive assembly 114 is configured such that the surgicalinstrument 62 can rotate, drive, or otherwise actuate a number ofdifferent types of surgical instruments, tools, modules, end effectors,and the like, which can be configured to engage and rotate concurrentlywith either the bore 122 of the driving cannula 116, or the coupling 126of the driving head 118. It will be appreciated that this configurationallows the same surgical instrument 62 to be utilized in a broad numberof medical and/or surgical procedures. However, it is contemplated thatthe drive assembly 114 could be configured differently in someconfigurations, such as to omit a driving head 118 with a coupling 126in configurations where the surgical instrument 62 configured fordedicated use with the drill bit 66 of the present disclosure.

Referring back to FIGS. 1-3 the illustrated configuration of thesurgical instrument 62 further comprises a release mechanism, orcoupling mechanism, generally indicated at 150, configured to facilitateremoval of the drill bit 66. The coupling mechanism 150 generallycomprises a release subassembly 152, a keeper body 154, and a housingadapter 156. The keeper body 154 and the housing adapter 156 arerespectively configured to secure the release subassembly 152 to theactuator assembly 82 and the handpiece body 74, and could be realizedwith a number of different configurations or could be integrated intoother parts of the surgical instrument 62 in some configurations.

As noted above, the drill bit 66 of the present disclosure generallyextends along the axis AX between the cutting tip portion 70 and theinsertion portion 72, and is configured for releasable attachment to thesurgical instrument 62 described herein and illustrated throughout thedrawings via engagement between the interface 124 of the drill bit 66and the bore 122 of the driving cannula 116 of the drive assembly 114.The driving cannula 116, in turn, cooperates with the output hub 96 ofthe gearset 86 of the actuator assembly 82 to facilitate rotating thedrill bit 66 about the axis AX.

Referring now to FIG. 2 , the drill bit 66 comprises a shank, generallyindicated at 176, which extends along the axis AX between a proximal end178 and a distal end 180. The distal end 180 of the shank 176 isprovided with flutes 182 which are helically disposed about the axis AXand extend to the tip of the drill bit 66 to promote workpiece, such astissue, penetration (see FIG. 2 ). In the illustrated configuration, thedrill bit 66 is also provided with a bearing region 184 coupled to theshank 176 between the proximal end 178 and the distal end 180. Thebearing region 184 is sized so as to be received within and rotaterelative to the measurement probe 134 of the measurement module 128.Here, the bearing region 184 essentially defines a “stepped” outerregion of the shank 176 that affords rotational support along the lengthof the drill bit 66, and has a larger diameter than adjacent distal andproximal regions of the shank 176 in the illustrated configuration.However, it will be appreciated that the bearing region 184 of the shank176 of the drill bit 66 could configured in other ways without departingfrom the scope of the present disclosure. Furthermore, while describedas a drill bit 66 in the present disclosure, it is also contemplatedthat the drill bit 66 could have similar features and be configured asanother suitable end effector, or rotary end-effector, such as a bur orreamer.

The illustrated configuration of the surgical system 60 furthercomprises the measurement module, generally indicated at 128, which maybe configured to releasably attach to the surgical instrument 62 toprovide the surgeon with measurement functionality during use. To thisend, and as is best shown in FIGS. 4 and 5 , the measurement module 128may generally comprises a housing 130, a guide bushing 132, ameasurement probe 134 (i.e., a probe or a measurement cannula), and asensor assembly, here a transducer assembly 136. The housing 130 may bereleasably attachable to the surgical instrument 62 and generallysupport the various components of the measurement module 128. Theillustrated housing 130 is formed as a pair of housing components 138which interlock or otherwise attach together, and may be configured fordisassembly to facilitate cleaning or servicing the measurement module128. It should be appreciated that the measurement module may be formedas an integral component of the surgical instrument as well.

In the illustrated configuration, the housing components 138 and theguide bushing 132 comprise correspondingly-shaped features arranged toprevent relative axial and rotational movement therebetween, such as vianotches formed in the guide bushing 132 which fit into webs or ribsformed in the housing components 138 (not shown in detail). The guidebushing 132 further comprise a window 142 for use with the transducerassembly 136 as described in detail below.

The measurement probe 134 may be disposed within the guide bushing 132and is supported for translational movement along the axis AX relativeto the handpiece. An elongated recessed slot 143 (partially depicted inFIG. 2 ) is formed transversely into the measurement probe 134 andextends longitudinally. While not specifically illustrated herein, theelongated recessed slot 143 is shaped and arranged to receive a travelstop element which, in turn, is supported by the housing 130 andlikewise extends through an aperture formed transversely through theside of the guide bushing 132; this arrangement serves both to limit howfar the measurement probe 134 can be axially extended or retractedrelative to the guide bushing 132, and also prevents the measurementprobe 134 from rotating about the axis AX. However, it will beappreciated that the measurement module 128 could be configured to limitor prevent movement of the measurement probe 134 in other ways withoutdeparting from the scope of the present disclosure.

As illustrated, the measurement probe 134 further comprises rack teeth144 which are disposed in meshed engagement with a gear 146 of thetransducer assembly 136. As shown in FIG. 5 , the window 142 of theguide bushing 132 is arranged adjacent to the transducer assembly 136 tofacilitate the meshed engagement between the rack teeth 144 and the gear146. The gear 146 includes a shaft portion 147 extending along a commongear axis CAX. The gear 146 itself is rotatable 360 degrees or moreabout the common gear axis CAX as the probe 134 moves along the axis AXrelative to the housing 130.

The transducer assembly 136 is responsive to rotation of the gear 146resulting from axial movement of the measurement probe 134 in order togenerate electrical signals representing changes in the position of themeasurement probe 134 relative to the housing 130 along the axis AX.Thus, it will be appreciated that the transducer assembly 136 is able toprovide the surgical instrument 62 with enhanced functionality. By wayof example, in some configurations, the transducer assembly 136 may bedisposed in communication with the controller 78, which may beconfigured to interrupt or adjust how the motor 84 is driven based onmovement of the measurement probe 134, such as to slow rotation of thedrill bit 66 at a specific drilling depth into the workpiece. Thetransducer assembly 136 may also be disposed in communication with anoutput device 148, such as a display screen, one or more light-emittingdiodes (LEDs), and the like, to provide the surgeon with informationrelating to movement of the measurement probe 134, such as to display areal-time drilling depth, a recorded historical maximum drilling depth,and the like. Other configurations are contemplated.

The controller 78 comprises one or more microprocessors for processinginstructions or for processing algorithms stored in memory to carry outthe functions described herein. Additionally or alternatively, thecontroller 78 may comprise one or more microcontrollers, subcontrollers,field programmable gate arrays, systems on a chip, discrete circuitry,and/or other suitable hardware, software, or firmware that is capable ofcarrying out the functions described herein. The controller 78 may becarried in the handpiece body 74 as illustrated in FIG. 5 , or elsewherein the surgical system 60, or may be remotely located. Memory may be anymemory suitable for storage of data and computer-readable instructions.For example, the memory may be a local memory, an external memory, or acloud-based memory embodied as random access memory (RAM), non-volatileRAM (NVRAM), flash memory, or any other suitable form of memory.

In certain embodiments, the controller 78 comprises an internal clock tokeep track of time. In one embodiment, the internal clock is amicrocontroller clock. The microcontroller clock may comprise a crystalresonator; a ceramic resonator; a resistor, capacitor (RC) oscillator;or a silicon oscillator. Examples of other internal clocks other thanthose disclosed herein are fully contemplated. The internal clock may beimplemented in hardware, software, or both. In some embodiments, thememory, microprocessors, and microcontroller clock cooperate to sendsignals to and operate the various components to meet predeterminedtiming parameters.

In the embodiment described herein, and as best shown in FIGS. 6-8 , thetransducer assembly 136 includes at least two rotational sensor devices,here shown as a pair of potentiometers 500, 501, which are positioned inproximity to one another within the housing portion 138. For ease ofdescription below, a pair of potentiometers 500, 501 are describedhereinafter.

As best shown in FIGS. 7-8 , each of the potentiometers 500, 501, whichmay be the same or different, are rotatable potentiometers and include abody portion 502 and a rotor portion 507 positioned within the bodyportion 502. The rotor portion 507 of each of the potentiometers 500,501 is coupled to the gear 146 via the shaft portion 147 and is thusrotatable as the gear 146 rotates about the common gear axis CAX. Thebody portion 502 is fixedly coupled to the housing portion 138, and thusdoes not rotate as the rotor portion 507 rotates. The body portion 502,in certain embodiments, is integral with the housing portion 138. Inparticular, the rotor portions 507 of the potentiometers 500, 501 arerotatable 360 degrees about the common gear axis CAC as the gear 146rotates. In other words, the potentiometers 500, 501 are of the typethat do not include stops (i.e., stop members) that limit the rotationof the rotor portions 507 relative to the body portions 502 to less than360 degrees of rotation. Stated still another way, the rotor portions507 are freely rotating with the gear 146.

The body portion 502 includes a pair of terminal portions 503, 504connected to a resistive element 505. The first terminal portion 503 isconnected (i.e., is electrically connected) to a power source, such asthe battery 76, and is supplied with a first reference signal (i.e., apredefined voltage) from the power source. The second terminal portion504 is connected to a second reference signal. In certain embodiments,the second reference signal is a ground. An inner channel (not shown) ofthe body portion 502 is provided to serve as the void for containingconductors (such as a flex circuit) that extend from the respectiveterminal portions 503, 504 and 506. The body portion 502 also includes athird terminal portion 506 that is connected (i.e., electricallyconnected) to the controller 78.

The rotor portion 507 of each of the potentiometers 500, 501 alsoincludes a wiper arm 508 that extends radially outward from the commongear axis CAX, with its radially outward end 512 configured to beconnected to (i.e., contact, or electrically connect) the resistiveelement 505 or to be positioned along the gap 511 depending upon itsrelative rotational positioning of the wiper arm 508 about the commongear axis CAX with respect to the body portion 502. Another portion ofthe wiper arm 508, shown here as the radially inward end 513 thatterminates at a point corresponding to the common gear axis CAX, isconnected (i.e., electrically connected) to the third terminal portion506. The gear 146 is connected to each one of the respective rotorportions 507 by way of the shaft portion 147. Therefore, the rotation ofthe gear 146 about the common gear axis CAX results in the like rotationof the wiper arms 508 of the potentiometers 500, 501 about the commongear axis CAX and about the respective static body portions 502.

The resistive element 505 may be arcuate in shape, defining an arcuatelength AL between the pair of terminal portions 503, 504, and ispositioned along a surface of the body portion 502 between the terminalportions 503, 504. A gap 511 extends along a portion of the body portion502 between the second terminal portion 504 and the first terminalportion 503 and defines an additional arcuate length AAL that does notinclude the resistive element 505.

As noted above, the length of the wiper arm 508, corresponding to theradius (r) of the wiper arm 508 from the radially inward end 513 to theradially outward end 512, is configured such that the radially outwardend 512 of the wiper arm 508 is connected to the resistive element 505or is positioned along the gap 511, and as such the arcuate length AL ofthe resistive element 502 and the additional arcuate length AAL of thegap 511 corresponds to the arc defined by the radially outward end 512of the wiper arm 508 as it rotates 360 degrees about the common gearaxis CAX. The total arcuate length of this arc, which corresponds to thesum of the arcuate length AL and the additional arcuate length AAL, isequal to 2πr, with r defined as the radial length of the wiper arm 508from the radially outward end 512 to the center of rotation CAX.

In certain embodiments, the arcuate length AL of the resistive element505 is less than or equal to 11 πr/6 (corresponding to less than orequal to 330 degrees of the 360 degrees of rotation of wiper arm 508 ina single rotation of the gear 146), while the corresponding arcuatelength AAL corresponding to the gap 511 is greater than or equal to πr/6and less than 2πr (corresponding to the remainder of the 360 degrees ofrotation of wiper arm 508 in a single rotation of the gear 146, i.e.,greater than or equal to 30 degrees and less than 360 degrees ofrotation in a single rotation of the gear 146), with the total lengthequal to 2πr as noted above.

When the wiper arm 508 of one or both of the potentiometers 500, 501 ispositioned such that it is in contact with the resistive element 505, anoutput signal is generated from the wiper arm 508 that is sent to thecontroller 78, with the output signal corresponding to the relativepositioning of the wiper arm 508 along the arcuate length AL of theresistive element 505 and scaled with respect to the received firstreference signal received by the resistive element from the firstterminal portion 503. The scale of the first reference signal receivedby the controller 78 through the wiper arm 508 and third terminalportion 506, as one of ordinary skill appreciates, is stronger when thewiper arm 508 is positioned nearer to the first terminal portion 103 andis progressively weaker as the wiper arm 508 is rotated to a positionnearer to the second terminal portion 504. Conversely, when the wiperarm 508 of one of the potentiometers 500, 501 is positioned within thegap 511, an interrupted signal or no signal is generated from the wiperarm 508 that is sent to the controller 78 (known as the floatingposition, corresponding to a high ohmic impedance). The generated outputsignal or signals received by the controller 78, or the interruptedsignals, are interpreted by the controller 78 through its storedalgorithms to determine the relative positioning of the probe 100relative to the housing 130, and thus use the information to determinethe relative depth of the bore in the workpiece, such as tissue or bone,formed by the drill bit, as will be explained further below.

As also illustrated in FIGS. 6-8 , the potentiometers 500, 501 arestacked adjacent to each other in the z-direction in a manner such thatthe wiper arm 508 of at least one of the pair of potentiometers 500, 501remains in contact with its respective resistive element 505 at alltimes, regardless of relative rotational positioning of wiper arms 508of the pair of potentiometers 500, 501. Accordingly, at all times, atleast one generated output signal via the wiper arm 508 in contact withthe resistive element 505 is received by the controller 78 that can beused to determine the relative depth of the bore in the workpiece formedby the drill bit, as will be explained further below.

To accomplish this, the body portion 502 of one of the potentiometers500 is rotatedly offset about the common gear axis CAX relative to thebody portion 502 of the other one of the potentiometers 501 such thatthe resistive element 505 of the second potentiometer 501 is alignedalong at least the entirety of the gap 511 of the first potentiometer500, when viewed in the z-direction, as in FIGS. 7 and 8 . This offsetrotational alignment of the resistive elements 505 may be confirmed bycomparing their relative alignments of the resistive elements 505, inthe z-direction as shown in FIGS. 7 and 8 with a reference point 146 aassigned on the circumference of the gear 146 as it rotates 360 degreesaround the common gear axis CAX.

The rotation of the body portion 502 of the second potentiometer 501about the common gear axis CAX relative to the body portion of the bodyportion 502 of the first potentiometer 500, as illustrated in FIGS. 7and 8 , may be defined in terms of the number of degrees of rotation asit relates to a Cartesian coordinate system. Accordingly, in FIG. 7A-7C,the x-axis in a Cartesian coordinate system is illustrated as right andleft, the y-axis in a Cartesian coordinate system is illustrated as upand down, and the z-axis may be defined as into and out of the page. Theup position may be designated at 0 degrees, with the down position at180 degrees, and with the right and left positions at 90 and 270degrees, respectively. By way of example, the rotation the body portion502 of the first potentiometer 500 one-hundred eighty degrees about thecommon gear axis CAX relative to the second potentiometer 501 (or viceversa) and fixing the body portion 502 in that configuration, such asshown in FIGS. 7A-7C, results in the terminal portions 503, 504, 506 ofthe respective potentiometers 500, 501 being positioned 180 degreesrotationally offset from one another (as shown in FIGS. 7A-7C, theterminal portions 503, 504, 506 of potentiometer 500 are positioned at180 degrees while the terminal portions 503, 504, 506 of potentiometer501 are positioned at 0 degrees). By way of a second example, as shownin FIG. 8 , rotating the first potentiometer 500 ninety degreescounterclockwise relative to the second potentiometer 501 about thecommon gear axis CAX, and fixing the body portions 502 in thatconfiguration, results in the terminal portions 503, 504, 506 of therespective potentiometers being positioned 90 degrees rotationallyoffset from one another (as shown in FIG. 8 , the terminal portions 503,504, 506 of potentiometer 500 are positioned at 0 degrees while theterminal portions 503, 504, 506 of potentiometer 501 are positioned at90 degrees). It should be appreciated that other rotational offsets ofthe potentiometers 500, 501 relative to one another about the commongear axis CAX are also contemplated, so long as the offset is sufficientto ensure that at least one wiper arm 508 of at least one of thepotentiometers 500, 501 is in contact with its resistive element 505. Incertain embodiments, the gap 511 between the terminal portions 503, 504corresponds to about 30 degrees of rotational offset, and accordinglythe rotational offsets may be anywhere from 30 to 330 degrees relativeto one another, such as 45 degrees, 60 degrees, 75 degrees, 105 degrees,120 degrees, 150 degrees, 210 degrees, 270 degrees, etc.

To do the comparison of the rotational offset of the respective elements505 of the pair of potentiometers 500, 501, the reference point 146 a isassigned to a relative position on the gear 146. For ease of descriptionand illustration, as provided in FIG. 7A, the reference point 146 a hasbeen assigned to a position on the gear 146 corresponding to theintersection of the resistive element 505 and the first terminal portion503 on the first potentiometer 500 when viewed from the z-direction. Thegear 146, for illustrative and description purposes, can be subdividedinto a first arcuate region 146 b and a second arcuate region 146 c,which together sum to 360 degrees of rotation (i.e., one full revolutionof the gear 146). The first arcuate region 146 b corresponds the arcuatelength AL of the resistive element 505 of the first potentiometer 500when viewed in the z-direction, while the second arcuate region 146 ccorresponds to the additional arcuate length AAL associated with the gap511 of the first potentiometer when viewed in the z-direction. The firstand second arcuate regions 146 b, 146 c, being static reference regions,do not rotate as the gear 146 and the reference point 146 a rotatesabout the common axis CAX, but maintain fixed coordination with thestatic arcuate length AL of the resistive element 505 and additionalarcuate length AAL of the gap 511 of the first potentiometer 500.

As the gear 146 rotates about the common gear axis CAX in a firstrotational direction, the reference point 146 a correspondingly rotatesalong an angular path of rotation AR (i.e., an arcuate path of rotation)about the common gear axis CAX through the first arcuate region 146 band the second arcuate region 146 c for every full revolution of thegear 146. As such, depending upon the relative amount of rotation of thegear 146 in the first rotational direction, the reference point 146 a iseither positioned in the first arcuate region 146 b or the secondarcuate region 146 c at all times as the gear 146 rotates 360 degreesabout the common gear axis CAX in the first rotational direction.

Referring first to FIG. 7A, the gear 146 is positioned such that thewiper arm 508 of the first potentiometer 500 is positioned at theintersection of the resistive element 505 and the terminal portion 503.At the same time, the wiper arm 508 of the second potentiometer 501 ispositioned on the resistive element 505 at a point between the first andsecond terminal portion 503, 504. In this position, the reference point146 a is in the first arcuate region 146 b of the gear 146, and bothwiper arms 508 generate output signals to the controller 78 through thethird terminal portion 506 by virtue of their electrical connection tothe respective resistive element 505, but wherein the scale of therespective output signals is different (assuming that the firstreference signal provided through the first terminal portion 503 of eachpotentiometer 500, 501 is the same) due to the positioning of therespective wiper arms 508 relative to their first and second terminalportions 503, 504.

In FIG. 7B, the gear 146 has rotated such that the positioning of thewiper arm 508 of the first potentiometer 500 is located at theintersection of the resistive element 505 and the second terminalportion 504 and such that the positioning of the wiper arm 508 of thesecond potentiometer is nearer to the first terminal portion 503 than inFIG. 7A. In this position, the reference point 146 a is still in thefirst arcuate region 146 b of the gear 146 (but at a different relativeposition than in FIG. 7A), and both wiper arms 508 generate outputsignals to the controller 78 through the third terminal portion 506 byvirtue of their electrical connection to the respective resistiveelement, but wherein the scale of the respective output signals isdifferent from the respective scales in FIG. 7A.

In FIG. 7C, the gear 146 has rotated such that the positioning of thewiper arm 508 of the first potentiometer 500 is located within the gap511 and such that the positioning of the wiper arm 508 of the secondpotentiometer 501 is along the resistive element 505 in a positioncloser to midway between the first and second terminal portions 503,504. In this position, the reference point 146 a is in the secondarcuate region 146 c of the gear 146, and only the wiper arm 508 of thesecond potentiometer 501 generates an output signal to the controller 78through the third terminal portion 506, but wherein the scale of therespective output signal is different from the respective scales inFIGS. 7A and 7B. Further, the output signal of the first potentiometer500 is interrupted, because there is no electrical contact between thewiper arm 508 and the resistive element 505, resulting in an open,floating condition giving a high (mega-ohm) impedance. As such, thecontroller 78 receives only an output signal from the secondpotentiometer 501 (and either receives an interrupted signal, or nosignal, from the first potentiometer 500).

While not illustrated, when the gear 146 is rotated such that the wiperarm 508 of the second potentiometer 501 is within the gap 511 (i.e.,between the terminal portions 503, 504 along the top of FIGS. 7A-7C, thewiper arm 508 of the first potentiometer 500 is located approximatelymidway between the first and second terminal portions 503, 504 along theresistive element 505, and the reference point 146 a is positioned inthe first arcuate region 146 b. Here, the output signal of the secondpotentiometer 501 is interrupted, because there is no electrical contactbetween the wiper arm 508 and the resistive element 505. As such, thecontroller 78 receives only an output signal from the firstpotentiometer 500 of approximately one-half of the first referencesignal provided through the first terminal portion 503 (and eitherreceives an interrupted signal, or no signal, from the secondpotentiometer 501).

As FIGS. 7A-7C illustrate, at each and every potential reference point146 a position as the gear 146 rotates 360 degrees, at least one of thewiper arms 508 of the respective potentiometers 500, 501 is electricallyconnected to its respective resistive element 505. Accordingly, at eachand every reference point position, a respective output signal isgenerated and sent to the controller 78 which can be used to determinethe relative depth of the bore in the workpiece formed by the drill bit,as will be described further below.

Still further, FIGS. 7A-7C confirm that when the reference point 146 ais in the first arcuate region 146 b, regardless of its relativeposition within the first arcuate region 146 b, the wiper arm 508 of thefirst potentiometer 500 is in electrical contact with its respectiveresistive element 505. Also, FIGS. 7A-7C confirm that when the referencepoint 146 a is in the second arcuate region 146 c, regardless of itsrelative position within the second arcuate region 146 c, the wiper arm508 of the second potentiometer 501 is in electrical contact with itsrespective resistive element 505. In other words, in the configurationof FIGS. 7A-7C, at least one wiper arm 508 of the respective pair ofpotentiometers 500, 501 is always in contact with its respectiveresistive element 505, regardless of the positioning of the referencepoint 146 a in either the first or second arcuate regions 146 b, 146 c.

In FIG. 8 , the body portion 502 of the second potentiometer 501 isrotated 90 degrees relative to the body portion 502 of the firstpotentiometer 500 (as opposed to 180 degrees as in FIGS. 7A-7C). Similarto the arrangement of FIGS. 7A-7C, the amount of rotation of the secondpotentiometer 501 relative to the first potentiometer 500 is sufficientto ensure that the gap 511 of the second potentiometer 501 is notaligned with the gap 511 of the first potentiometer 500.

Accordingly, as illustrated in the embodiments herein, in order toaccomplish this stacking effect with the rotationally offset resistiveelements 505, the potentiometers 500, 501 are coupled to the gear shaft147 such that their body portions 502 are coupled to the housing portion138 are rotationally offset sufficiently to ensure that the gap 511 ofthe second potentiometer 501 is not aligned with the gap 511 of thefirst potentiometer 500. In other words, if the arcuate length AL of theresistive element 505 of each of the first and second potentiometers500, 501 is 11 πr/6 (and hence the gap 511 is πr/6), the rotatedpositioning of the body portion 502 of the second potentiometer 501between 30 and 330 degrees (which correlates to between πr/6 and 11πr/6) about the common gear axis CAX ensures that gaps 511 of the firstand second potentiometers 500, 501 do not overlap when another whenviewed from the z-direction.

Stated another way, while FIGS. 7 and 8 illustrate the body portions 502of the pair of potentiometers 500, 501, rotated at 180 and 90 degreesoffset from one another, other rotational offsets of the potentiometers500, 501 are contemplated. Specifically, the body portions 502 of thepair of potentiometers 500, 501 may be offset from 30 to 330 degreesabout the common gear axis CAX, and fixing the body portions 502 in thatconfiguration, which ensures that at least one of the wiper arms 508(rotating in coordination with one another) is contacting its respectiveresistive element 505 at all relative positions of the reference point146 a of the gear 146. In other words, through the use of two pairedpotentiometers 500, 501 as described above, represented in twoembodiments in FIGS. 7 and 8 , at least one of the pair ofpotentiometers 500, 501 will be in the non-floating condition at alltimes, regardless of the rotational positioning of the wiper arms 508 ofthe potentiometers 500, 501, and thus is capable of providing a validreading that can be used by the controller 78 to determine the boredepth as can be determined according to the method described below. Itis of course possible to use three or more potentiometers in this manneras well.

Referring next to FIGS. 9 and 10 , a method for determining a bore depthin a workpiece formed by a drill bit 66 in the drill 60 as describedabove is also provided. In general, as illustrated in FIG. 9 , the logic700 for determining the bore depth includes three basic steps. First, inStep 702, the drill 60 is positioned against the workpiece. Inparticular, the drill 60 is positioned such that the cutting tip portion70 at distal end 180 of the drill bit 66 is placed against theworkpiece. Next, in Step 704, the drill 60 is actuated to advance thecutting tip portion 70 of the drill bit 66 into the workpiece to form abore, or hole, having a bore depth. As a part of Step 704, thecontroller 78 directs the power source to send a first reference signal(typically in the form of a reference voltage), through the firstterminal portion 503 to each of the respective resistive elements 505 ofthe potentiometers 500, 501. Finally, in Step 706, the bore depth isdetermined via the controller 78 by determining the total amount ofmovement of the probe relative to the housing during Step 704. Step 706can be determined after completion of the drilling of the hole, by thedrill 60, or can be determined at any point in time as the hole is beingdrilled, with the instantaneous bore depth being determined andcontinuously updated.

In FIG. 10 , the details of the logic of Step 706 are described infurther detail. First in Step 708, the controller 78 determines theinitial, or first, rotational position of the reference point 146 a ofthe gear 146, in certain cases, prior to said step of actuating thedrill 60. In particular, the initial rotational position of thereference point 146 a of the gear 146 can be determined based upon therespective positioning of the at least two wiper arms 508 as the drill60 is positioned against the workpiece in Step 702 prior to theactuation of the drill 60 in Step 704. In this position, an initialrespective signal(s) is generated from at least one of the at least twowiper arms 508, with each signal scaled to their respective positioningon the resistive element 505 as a function of the respective providedfirst reference signal. The controller 78 receives the initialrespective signal(s) and determines the initial respective position ofthe reference point 146 a of the gear 146 on the basis of the receivedinitial respective signal(s). To aid in determining the initialrespective position of the reference point, the memory of the controller78 includes stored information regarding the size of the gear 146 andincludes a pre-stored algorithm that can interpret the scale of thereceived initial inputs signal(s) and identify the relative positioningof the reference point 146 a of the gear 146 corresponding to the scaleof the received initial inputs signal(s).

In Step 710, the controller 78 determines a number of full rotations ofthe gear 146 in a single rotational direction about the common gear axisCAX with the at least two potentiometers 500, 501 during, or after, saidstep of actuating the drill.

More specifically, the controller 78 determines a number of distinctinterrupted signals generated from the wiper arm 508 of one, or both, ofthe potentiometers 500, 501 during Step 710. Each interrupted signaloccurs when the gear 146 is rotated in the single rotational directionsuch that the reference point 146 a of the gear 146 is within the secondarcuate region 146 c such that the wiper arm 508 of a designated one orboth of the potentiometers 500, 501 (typically the first potentiometer500) is within the gap 511. The end of one interrupted signal occurswhen the gear 146 is further rotated in the single rotational directionsuch that the wiper arm 508 initiates contact with the resistive element505 at the location corresponding to the first terminal portion 503, orthe second terminal portion 504, depending upon which direction thewiper arm 508 is rotating about the common gear axis CAX.

In Step 712, the controller 78 determines a final, or second, rotationalposition of the reference point 146 a of the gear 146 after Step 704 orat any point during step 704. In particular, the final rotationalposition of the reference point 146 a of the gear 146 can be determinedbased upon the respective positioning of the at least two wiper arms 508after the actuation of the drill is terminated. In this position, afinal, second respective signal is generated from at least one of the atleast two wiper arms 508, with each signal scaled to their respectivepositioning on the resistive element 505 as a function of the respectiveprovided first reference signal. The controller 78 receives the final,second respective signal(s) and utilizes the algorithm stored in thememory of the controller 78 to determine the final respective positionof the reference point 146 a of the gear 146 on the basis of thereceived final, second respective signal(s).

In Step 714, the controller 78 determines a change in the rotationalposition of the reference point 146 a of the gear 146 between saiddetermined initial, first rotational position of Step 710 and saiddetermined, second final rotational position of Step 712. Morespecifically, the controller 78 compares the received initial, firstrespective signal(s) and the received final, second respective signal(s)and calculates the change in positioning based on the compared signalsutilizing an algorithm stored in the memory of the controller 78.

Finally, in Step 716, the controller 78 determines the bore depth fromthe determined number of full rotations of the gear 146 occurring duringStep 712 and from the determined change in the rotational position ofthe reference point 146 a of the gear 146 in Step 714. Morespecifically, the controller 78 utilizes an algorithm stored in itsmemory that calculates the relative amount of movement of the probe 100relative to the housing 130 on the basis of the determined number ofinterrupted signals and on the determined change in the rotationalposition of the reference point 146 a of the gear 146 and furthercalculates the bore depth on the basis of the determined relative amountof movement. As a part of Step 716, the controller 78 may send an outputsignal to the display 148, which provides a reading on the displaycorresponding to the bore depth that is visible by the operator of thedrill 60.

In each of the Steps for the logic 700 of FIG. 10 , the controller 78may be configured to determine the initial, first and final, secondpositioning of the reference point 146 a of the gear 146 on the basis ofany single one received initial respective signal, and any single onereceived final respective signal, or on the basis of both receivedinitial respective signals or both received final respective signals(i.e., based on the combined received initial respective signals orcombined received final respective signals, when both of the wiper arms508 are in contact with the respective resistive elements 505corresponding to the initial and final respective position of thereference point 146 a), to determine the initial and final positioningof the reference point 146 a of the gear 146.

In still further embodiments, the controller 78 is configured toconfigured to continually process generated signals from received fromeach of the potentiometers 500, 501 during Step 710 to continuallydetermine the respective positioning of the reference point 146 a of thegear 146. In this regard, the controller 78 may utilize the receivedsignal from one of the potentiometers 500 or 501 as the primary signalto continually determine the relative positioning of the reference point146 a of the gear 146, and only utilizing the signal received from thesecond one of the potentiometers 500 or 501 when the primary signal isin the interrupted state (i.e., where the wiper arm 508 of thedesignated one of the potentiometers 500 or 511 is positioned within thegap 511).

Still further, the controller 78 may be configured to determine thenumber of complete revolutions of the gear 146 on the basis of thenumber of interrupted signals from a respective one of thepotentiometers 500 or 501, or on the basis of the number of interruptedsignals from both of the potentiometers 500, 501.

In further embodiments, as opposed to having a pair of potentiometers500, 501 stacked in the z-direction as illustrated in FIGS. 7 and 8 ,the potentiometers 500, 501, could be positioned side-to-side in thex-direction. For example, an additional gear (not shown) could be meshedwith the gear 146. A gear shaft from the additional gear could then becoupled to the rotor portion 307 of the second potentiometer 501. Therotation of the gear 146 would in turn rotate the additional gear, andboth wiper arms 508 of the first and second potentiometers 500, 501would rotate as described above. In a manner similar to the embodimentsof FIGS. 7 and 8 above, by positioning the body portion 502 of thesecond potentiometer 501 such that at least one of the wiper arms 508 isalways in contact with its respective resistive element 505

The surgical system 60 described herein provides a method for accuratelymeasuring the bore depth in a workpiece formed by the drill bit 66 ofthe drill while also addressing the deficiencies with surgical drillsutilizing a single potentiometer. Specifically, by utilizing at leasttwo potentiometers which are configured such that at least one of thewiper arms is in contact with its respective resistive elementregardless of the positioning of the reference point of the gear, thefloating condition can be avoided. Still further, the inclusion of theat least one additional potentiometer makes it unnecessary to increasethe diameter of the gear size to ensure that the gear, and the coupledsingle turn potentiometer, do not turn such that the wiper arm ispositioned within the gap. This overcomes the further deficiencies ofsurgical drills having a single potentiometer in terms of undesirablebulk to the drill and potential obstruction of the surgeon's field ofvision during the drilling operation.

It should be appreciated that the system described herein may be usedfor non-surgical applications, such as through drilling throughworkpieces other than tissue, such as wood, metal, or plastic.Additionally, it should be appreciated that the system may be used inconjunction with end-effectors other than drill bits.

Several configurations have been discussed in the foregoing description.However, the configurations discussed herein are not intended to beexhaustive or limit the disclosure to any particular form. Otherconfigurations are specifically contemplated. For example, while the useof at least two potentiometers in the transducer assembly are describedherein in which the first of potentiometers is incapable of detecting areference point in the second arcuate region of the gear is describedabove but wherein the second potentiometer does detect the referencepoint in the second arcuate region, it is contemplated additionalpotentiometers, and not a single pair of potentiometers, may be utilizedsuch that at least one potentiometer is able to detect a rotationalposition of the reference point of the gear at all positions within thefirst and second arcuate regions. Moreover, while the potentiometers orrotational sensor devices described above are typically of the samedesign, potentiometers or rotational sensor devices of different typesor sizes may be utilized. Still further, other types of sensor deviceslocated on the surgical drill, such as Hall sensors or the like, may beutilized in conjunction with the rotational sensors described hereinthat could provide enhanced precision for measurement. Even stillfurther, it is contemplated that separate gears could be independentlycoupled to the probe, with each of the separate gears coupled to one, ormore than one, potentiometer, and configured to ensure precisemeasurement of the bore depth and each possible probe position relativeto the housing in accordance with the configuration of rotational sensordevices as described above. Still further, while the configurations forthe transducer assemblies described above are specifically illustratedwith respect to a removable measurement module, it is contemplated thatthe transducer assembly including the gear and sensor device may beincluded on a non-removable portion of the surgical drill.

The terminology which has been used is intended to be in the nature ofwords of description rather than of limitation. Many modifications andvariations are possible in light of the above teachings and thedisclosure may be practiced otherwise than as specifically described.

It will be further appreciated that the terms “include,” “includes,” and“including” have the same meaning as the terms “comprise,” “comprises,”and “comprising.” Moreover, it will be appreciated that terms such as“first,” “second,” “third,” and the like are used herein todifferentiate certain structural features and components for thenon-limiting, illustrative purposes of clarity and consistency.

The disclosure is intended to be defined in the independent claims, withspecific features laid out in the dependent claims, wherein thesubject-matter of a claim dependent from one independent claim can alsobe implemented in connection with another independent claim.

The present disclosure also comprises the following clauses, withspecific features laid out in dependent clauses that may specifically beimplemented as described in greater detail with reference to theconfigurations and drawings above.

-   I. A measurement module configured for releasable attachment to a    surgical instrument, said measurement module comprising:    -   a housing;    -   a measurement cannula;    -   a transducer assembly including a gear coupled to said        measurement cannula and configured to rotate more than 360        degrees about a gear axis upon the movement of said probe        relative to said housing, said gear having a reference point        having an angular path of rotation about said gear axis being        divided into a first arcuate region and a second arcuate region,        said first arcuate region being separate from said second        arcuate region; and    -   a transducer comprising at least two potentiometers, each of        said at least two potentiometers coupled to said gear,    -   a first of said at least two potentiometers configured to detect        a rotational position of said reference point in said first        arcuate region and a second of said at least two potentiometers        configured to detect said rotational position of said reference        point in at least said second arcuate region, said first        rotational sensor being incapable of detecting said reference        point in the second arcuate region.-   II. A measurement module configured for releasable attachment to a    surgical instrument, said measurement module comprising:    -   a housing;    -   a measurement cannula;    -   a transducer assembly including:    -   a gear coupled to said measurement cannula and configured to        rotate more than 360 degrees about a gear axis upon the movement        of said measurement cannula relative to said housing, said gear        having a reference point having an angular path of rotation        about said gear axis being divided into a first arcuate region        and a second arcuate region, said first arcuate region being        separate from said second arcuate region; and    -   a transducer comprising at least two rotational sensor devices,        each of said at least two rotational sensor devices fixed        rotationally relative to said gear,    -   a first rotational sensor device configured to detect a        rotational position of said reference point in said first        arcuate region and a second rotational sensor device configured        to detect said rotational position of said reference point in        said second arcuate region, said first rotational sensor device        being incapable of detecting said reference point in the second        arcuate region, said at least two rotational sensor devices each        being adapted for independently generating a output signal        corresponding to said detected rotational position of said        reference point in said respective first and second arcuate        region:    -   a controller configured to receive each of said independently        generated output signals and, based on each of said        independently generated output signals, determine the depth of        the bore in the tissue formed by the drill bit.-   III. A transducer assembly for use with a surgical tool having a    probe and a housing, said transducer assembly comprising:    -   a gear coupled to the probe and configured to rotate more than        360 degrees about a gear axis upon the movement of the probe        relative to the housing, said gear having a reference point        having an angular path of rotation about said gear axis being        divided into a first arcuate region and a second arcuate region,        said first arcuate region being separate from said second        arcuate region; and    -   a transducer comprising at least two potentiometers, each of        said at least two potentiometers coupled to said gear,    -   a first of said at least two potentiometers configured to detect        a rotational position of said reference point in said first        arcuate region and a second of said at least two potentiometers        configured to detect said rotational position of said reference        point in at least said second arcuate region, said first        potentiometer being incapable of detecting said reference point        in the second arcuate region.

What is claimed is:
 1. A measurement module configured for releasableattachment to a surgical instrument, said measurement module comprising:a housing; a measurement probe; a transducer assembly including a gearcoupled to said measurement probe, and configured to rotate more than360 degrees about a gear axis upon movement of said measurement proberelative to said housing, said gear having a reference point having anangular path of rotation about said gear axis being divided into a firstarcuate region and a second arcuate region, said first arcuate regionbeing separate from said second arcuate region; and the transducerassembly comprising at least two potentiometers, each of said at leasttwo potentiometers coupled to said gear, a first of said at least twopotentiometers configured to detect a rotational position of saidreference point in said first arcuate region and a second of said atleast two potentiometers configured to detect said rotational positionof said reference point in at least said second arcuate region, saidfirst of said at least two potentiometers being incapable of detectingsaid reference point in the second arcuate region.
 2. The measurementmodule of claim 1, wherein said at least two potentiometers are adaptedfor independently generating an output signal corresponding to saiddetected rotational position of said reference point in said respectivefirst and second arcuate regions.
 3. The measurement module of claim 2,further comprising a controller coupled to each of said at least twopotentiometers and configured to receive said output signals and, basedon said output signals, determine an amount of movement of said proberelative to said housing.
 4. The measurement module of claim 3, furthercomprising a display, wherein said controller is configured to generatea bore depth signal that is received by said display corresponding tosaid bore depth signal, with said bore depth signal being presented onsaid display for viewing by a user.
 5. The measurement module of claim1, wherein each one of said at least two potentiometers comprises: abody portion having a pair of terminal portions electrically connectedto a resistive element, with one of said pair of terminal portionsconfigured to receive a first reference signal and another one of saidpair of terminal portions connected to a second reference signal, saidresistive element having an arcuate shape defining an arcuate lengthbetween said pair of terminal portions, said pair of terminal portionsseparated by a gap defining an additional arcuate length, and a rotorportion coupled within said body portion and coupled to said gear, saidrotor portion including a wiper arm electrically connected to a thirdterminal portion of said body portion, wherein the rotation of said gearabout said gear axis causes said wiper arm to rotate about said gearaxis, wherein a positioning of said wiper arm along said arcuate lengthof said resistive element generates an output signal at said thirdterminal portion, with said output signal corresponding to a relativepositioning of said wiper arm along said arcuate length of saidresistive element and scaled with respect to said first referencesignal, wherein a positioning of said wiper arm within said gapgenerates an interrupted signal, and wherein said wiper arm ispositioned so as to connect to said resistive element along said arcuatelength corresponding to rotational positions of said reference point ofsaid gear as said gear rotates 360 degrees about said gear axis.
 6. Themeasurement module of claim 5, further comprising a controller coupledto each of said at least two potentiometers and configured to receiveoutput signals independently generated by said at least twopotentiometers and, based on said independently generated outputsignals, determine a depth of a bore in tissue formed by a drill bit. 7.The measurement module of claim 6 wherein each wiper arm of said atleast two potentiometers is positioned so as to be electricallyconnected with its respective resistive element at at least onerotational position of said reference point of said gear, wherein eachwiper arm of said at least two potentiometers generates a respectiveoutput signal corresponding to its relative positioning along saidarcuate length of its respective resistive element and scaled withrespect to said first reference signal, and wherein said controller isconfigured to receive and combine said output signals from each wiperarm of said at least two potentiometers and, based on said outputsignals, determine an amount of movement of said probe relative to saidhousing.
 8. The measurement module of claim 7, wherein each one of saidwiper arms generates a respective output signal corresponding to itsrelative positioning along said arcuate length of its respectiveresistive element and corresponding to said received first referencesignal, and, wherein said controller is configured to receive saidoutput signals and select one of said output signals and, based on saidone of said output signals, determine an amount of movement of saidprobe relative to said housing.
 9. The measurement module of claim 6,wherein when said wiper arm of a single one of said at least twopotentiometers is positioned so as to be connected with its respectiveresistive element, said controller is configured to receive a generatedcorresponding output signal from said single one of said at least twopotentiometers and, based on said generated corresponding output signal,determine an amount of movement of said probe relative to said housing.10. The measurement module of claim 6, wherein said controller isfurther configured to determine a number of full revolutions of saidgear rotating about said gear axis, with each full revolutioncorresponding to a predefined amount of movement of said measurementprobe relative to said housing, and, based on each of said outputsignals and each of said interrupted signals and said number of fullrevolutions, determine a total amount of movement of said probe relativeto said housing.
 11. The measurement module of claim 6, wherein saidcontroller is also configured to determine a number of full revolutionsof said gear rotating about said gear axis, with each full revolutioncorresponding to a predefined amount of movement of said probe relativeto said housing, and, based on each of said generated correspondingoutput signals and each of said generated interrupted signals and saiddetermined number of full revolutions, determine a total amount ofmovement of said probe relative to said housing.
 12. The measurementmodule of claim 5, wherein said arcuate length of said resistive elementon said body portion of each of said at least two potentiometers is lessthan or equal to 11πr/6, wherein r is a radial length of each respectivewiper arm.
 13. The measurement module of claim 5, wherein said bodyportion of one of said at least two potentiometers is rotated about saidgear axis from greater than 0 degrees to less than 360 degrees relativeto said body portion of another one of said at least two potentiometers.14. The measurement module of claim 5, wherein said body portion of oneof said at least two potentiometers is rotated about said gear axis from30 to 330 degrees relative to said body portion of another one of saidat least two potentiometers.
 15. The measurement module of claim 5,wherein said body portion of one of said at least two potentiometers isrotated about said gear axis 180 degrees relative to said body portionof another one of said at least two potentiometers.
 16. The measurementmodule of claim 5, wherein each wiper arm of said at least twopotentiometers is positioned so as to be electrically connected with itsrespective resistive element at at least one rotational position of saidreference point of said gear.
 17. The measurement module of claim 1,wherein said measurement probe is a cannula.
 18. A measurement moduleconfigured for releasable attachment to a surgical instrument, saidmeasurement module comprising: a housing; a measurement probe; atransducer assembly including: a gear coupled to said measurement probeand configured to rotate more than 360 degrees about a gear axis uponmovement of said measurement probe relative to said housing, said gearhaving a reference point having an angular path of rotation about saidgear axis being divided into a first arcuate region and a second arcuateregion, said first arcuate region being separate from said secondarcuate region; and a transducer comprising at least two rotationalsensor devices, each of said at least two rotational sensor devicesfixed rotationally relative to said gear, a first rotational sensordevice configured to detect a rotational position of said referencepoint in said first arcuate region and a second rotational sensor deviceconfigured to detect said rotational position of said reference point insaid second arcuate region, said first rotational sensor device beingincapable of detecting said reference point in the second arcuateregion, said at least two rotational sensor devices each being adaptedfor independently generating an output signal corresponding to saiddetected rotational position of said reference point in said respectivefirst and second arcuate regions: a controller configured to receiveeach of said output signals and, based on each of said independentlygenerated output signals, determine a depth of a bore in tissue formedby a drill bit.
 19. The measurement module of claim 18, wherein saidfirst rotational sensor device is a potentiometer and said secondrotational sensor device is a second potentiometer.
 20. The measurementmodule of claim 18, further comprising a display, wherein saidcontroller is configured to generate a bore depth signal that isreceived by said display corresponding to said depth of the bore, withsaid bore depth signal being presented on said display for viewing by auser.